While water is an essential element for survival of living organisms, most diseases spread due to poor water quality, particularly due to the presence of bacteria and viruses in the water. Hence it is utmost important to purify the water before its use. There are several methods of water purification like chlorination, iodation, ozonation, UV-purification reverse osmosis and silver ions. Chemical purification like addition of chlorine, iodine or ozone has several disadvantages. For example, excess chlorination leads to cancer. Other methods like UV-purification and reverse osmosis are not cost effective. Ever since silver has been recognized as an antibactericide, its application in purification of water is increasing.
U.S. Pat. No. 4,608,247 discloses the use of silver in water purification wherein silver micro crystals on α-Al2O3 with a copper sheath surrounding it has a capability of Ag and Cu to leach into a swimming pool by galvanic action without application of electric current. U.S. Pat. No. 6,758,345 discloses treatment medium comprising silver deposited on to an alumina substrate useful for controlling microorganism in water effectively. Another US patent discloses silver and a second metal say Pd co-deposited on alumina as an effective catalyst in controlling the microorganism in water. Copending Indian patent application 1055/DEL/03 discloses a process of making silver on activated carbon by in-situ deposition using low voltage current for controlling microorganism in water.
The main drawbacks of the prior art patents is that alumina various impurities in water on contact for a long time because of its acidic character and also activated carbon is not a high strength material. Moreover in activated carbon the micro pores are not accessible for depositing silver ions. However both these supports alumina and carbon have advantages like high mechanical strength possessed by alumina and high inertness of carbon towards various impurities present in water. Also carbon is known to be deodorizer and decolorizing agent.